In a conventional bonding method of a light-emitting diode chip, such as the disclosure in U.S. Pat. No. 5,376,580, bubbles are easily produced at the bonding interface, so the bonding interface is easily separated during the manufacturing process, the yield is reduced, and the light-emitting diode is difficult to be produced massively.
For example, FIGS. 1a through 1d are schematic flow diagrams showing the process for manufacturing a conventional light-emitting diode. A substrate 100 is provided. An n-type semiconductor layer 102, an active layer 104 and a p-type semiconductor layer 106 are grown on the substrate 100 by an epitaxy method in sequence, in which the n-type semiconductor layer 102, the active layer 104 and the p-type semiconductor layer 106 comprise an illuminant epitaxial structure 108, such as shown in FIG. 1a. The substrate 100 may be made of sapphire.
An electrically conductible substrate 110 is provided, and an adhesion layer 112 is formed on a surface of the substrate 110, such as shown in FIG. 1b. Next, a wafer bonding step is performed to adhere the substrate 110 to the p-type semiconductor layer 106 by the adhesion layer 112 for achieving the connection of the substrate 110 and the illuminant epitaxial structure 108, such as shown in FIG. 1c. Then, the electrically insulating substrate 100 is removed to complete the manufacturing of a light-emitting diode 114, such as shown in FIG. 1d. 
However, in such a bonding technique, bubbles are easily produced at the bonding interface between the illuminant epitaxial structure 108 and the adhesion layer 112 when the bonding step is performed. The existence of the bubbles greatly degrade the bonding strength. Due to the insufficient bonding strength, the substrate 110 very easily falls off the illuminant epitaxial structure 108 or chip, thereby degrading the yield of the sequent processes.